1. Field of the Invention
The invention relates to food product cans provided with can end members which may be opened easily by tearing with a ring pull tab, a full opening removable panel portion from the can end to which panel portion the tab is riveted, the tearing proceeding along an endless score line formed in the can end member which defines the panel; and more particularly to providing unusual stiffness and strength in relatively thin sheet metal material used to manufacture the ring pull tab, which strength is imparted by a special coordinated configuration, shape, contour and design of formed metal portions of the pull tab while at the same time requiring a minimum amount of metal; such pull tab structure being universal in use, either for a plain can end or a can end provided with a protective fold at the peripheral edge of the removed panel.
2. Description of the Prior Art
Many prior patents show various designs, shapes and configurations of ring pull tabs adapted to be riveted to end members of full panel pull-out ends of cans used particularly in the food products industry, such as U.S. Pats. Nos. 3,762,596, 3,838,788, 3,891,117 and 3,941,277. The ring pull tabs shown in each of said patents have the same general shape or outer perimeter configuration. Each is lanced partially around the rivet connection of the pull tab to the can end. The lance is formed in the body of the pull tab which extends from a complete circular ring portion, and the body is surrounded by a connected upwardly directed wall, part of which is connected to the complete ring. The various pull tabs shown in said patents have specifically different structures and are used as described in said patents for both plain and protective fold-containing can end panels.
Further, the various pull tabs shown in said patents all are adapted to be fabricated in progressive die press equipment having multiple lines such that a plurality, such as four pull tabs, are produced by the press with each stroke of the press, and up to 11 or more operations are carried out progressively in each line of the multiple lines during each stroke of the press.
Another type of pull tab involves a variation in the general structure of those pull tabs shown in the foregoing patents which eliminates the body of the pull tab and the lance formed in such body. The modified prior pull tab has a generally oval shape with an inner opening extending substantially the length of the oval and having an ear extending directly from the nose within the oval opening. The ear is riveted to the removable panel, and a pull tab of this type is shown in U.S. Pat. No. 3,799,390.
The oval pull tab structure also is adapted for fabrication in progressive die press equipment. However, the oval pull tab structure has been found to be weak. It frequently bends and fails across the frame-like portion defining the oval opening just behind the nose at either side of the rivet. Such failure results in inability to rupture the can end at the score line. This has led to the provision of a mustache-like cut or score in the can end between the rivet and the pull-out score line to be ruptured, in an attempt to reduce the amount of force required to be exerted by the pull tab for rupturing the can end along the pull-out score line.
The provision of the mustache-cut or score is not desirable since it reduces the integrity of the can when closed and filled with processed food for distribution and sale.
It is possible to eliminate the mustache cut and its disadvantages and to strengthen the oval-type pull tab by increasing the gauge and thus the amount of metal used in the manufacture of the pull tab. This expedient, however, results in a higher pull tab unit cost, and an increase in the amount of metal used, whereas an objective in the industry is to reduce the amount of metal required for pull tab manufacture while providing necessary strength.
Increased strength by the use of heavier gauge metal has the further disadvantage of requiring a complete redesign of the dies used in the progressive die equipment for fabricating the pull tabs.
These problems have been aggravated further by new specifications in the industry for increasing the metal thickness existing at the bottom of the pull-out score line, termed "increased residual", in order to increase the integrity of a can containing processed food against accidental rupture from any cause, such as during shipment of cans stacked on one another in shipping cartons distributed from a canner to wholesale houses or retail stores, or when cans are stacked on the display or stock counters of retail stores.
The accumulation of these existing complicated and interrelated difficulties concerning pull tabs for easy opening cans of the full panel pull-out type has resulted in a complex problem, and thus an existing need in the art for a pull tab which has increased strength using the same gauge metal, or which has the same strength with the use of reduced gauge metal, or which, disregarding gauge, has increased strength with the use of less metal as compared with the described prior types of pull tabs.
A further problem existing in the art relates to the need for what may be termed a universal pull tab structure, which may be used selectively, either for a plain can end, or for one containing a protective fold which is retained at the peripheral edge of the removed panel when removed.